Tri-metric erratic readings?

icarus
icarus Solar Expert Posts: 5,436 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I have been getting some erratic readings on my Tri-metric. Here is a copy of a note I sent to Bogart.

I have a 2020 that has been in service for about 5 years, and it has worked flawlessly. Just recently, it has started to read erratically on the amps scale, particularly under load. We live off grid in Northern Canada, and we have very small loads. When the draw is ~5 amps (12vdc) the meter will bounce around from 1-5 amps. When you scroll through the meter fields and come back to the amps field, it reads correctly for a while before bouncing around again. I have no idea if the ah down numbers and percentage of charge numbers are correct now or not either.

Do you have any suggestions, perhaps a shunt issue?

Thank You,

Tony
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Tri-metric erratic readings?

    Certainly check the cable connections (loosen and re-tighten screws). They are only measuring milli-volts or less. Any resistance, corrosion, bad connections can make for unstable readings.

    Have you installed any radio transmitters near the shunt/cabling/Trimetric lately?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #3
    Re: Tri-metric erratic readings?

    That fact that you change the control indicator and come back around to amps and it stays correct for a while would seem to point to the TM2020.

    Have you left it on volts reading for a while to check that reading stays solid?

    When I talked to the guy at Trimetrics he mentioned an electrolytic cap used to filter the amps reading. I remarked that an electrolytic may develope leakage as it gets old that may effect the reading. He said they have not seen such a problem.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Tri-metric erratic readings?

    Bill,

    No radio transmitter installed!

    RC, The voltage seems stable and agrees with my DVM and the Rogue metering.

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Tri-metric erratic readings?

    I was typing about the two meter leads that go from the shunt to the battery monitor. Those only read milli-volt or less and any type of poor connection will throw the "current" readings of the meter way off... With corrosion, it is even possibly for you to get a "battery" voltage source at the connection and causing an offset voltage to the monitor.

    Check the back of the Trimetric itself for good connections (and if you can see it, that there are no solder fractures from the connections to PCB connections). It is possible that just your pushing buttons on the meter is moving the wire/moving a solder fracture just enough to make a temporary connection.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #6
    Re: Tri-metric erratic readings?

    In your case the filter cap may be going open.

    If the filter is not there, the ADC will read erratic points on the full wave rectified sinewave shaped current profile from the shunt showing a different reading everytime it samples.

    You can try putting an external RC low pass filter on the wiring from the shunt. I believe the low pass filter in the unit is about 1 hz or less. Like a 1.5k with a 100 uF cap.

    You can call Trimetrics, its a small operation. The owner is pretty nice. He will probably tell you which cap and where it is on the PCB. He might even send you a replacement unit.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #7
    Re: Tri-metric erratic readings?

    Just got a note back from Ralph at Bogart:

    "ello Tony

    This could be a problem with wiring from the PentaMetric to the shunt. A wire that has become open, or flaky could cause this symptom. Also, I have seen situations where the 9 pin green connector has developed a high resistance to one connection. To check this you could remove, and insert the 9 pin green connector in the PM-5000-U input unit--wiggle it a little--a little friction on the pins may clear up the problem. First, check the connector, then inspect the wires from the shunt that is giving the wrong data--to the meter.

    We have occasionally (recently) seen some units that have had a part go bad (TLC27M4CN) in the Input unit. Apparently we may have gotten a batch of these parts that had an unusual number of failures. (Although I don't think that was as long as 5 years ago.) This could be the problem if you note the problem on ALL the amps readings, instead of just one. If it is just one channel, and the others are OK more likely the first explanation is correct. In that case we will need to fix it here.

    And indeed, if the amps are not correct, you cannot trust the ah numbers or percent of charge readings--since they depend on correct amps readings.

    Yours truly, Ralph Hiesey"

    Not bad customer service I think,

    Tony
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #8
    Re: Tri-metric erratic readings?

    If you have a DVM with 200 mVdc scale you can put it on shunt wires and see if it reads erratic or solid. If erratic then it's shunt. If solid then it is TM2020.

    If its a 500 amp shunt you may have to load up your inverter to get a decent reading.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
    Re: Tri-metric erratic readings?

    I been in further contact with Ralph at Bogart. It seems that is in all likely hood a wiring problem. I took all the wires off the shunt and the back of the meter, and it all seems fine now. BTW, Ralph offered to take the unit back to look it over, even though it is way out of warrantee. I am very impressed with how they do business.

    Tony
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